Blizzard in Alaska, March 5, 2009

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
500 AM AKST THU MAR 5 2009

.MODEL DISCUSSION...

THE 00Z GFS INITIALIZED WELL AND CONTINUES TO HANDLE THE EVOLUTION OF
THE CURRENT SYSTEM SATISFACTORILY.  THE COLD FRONT SHOULD PASS
THROUGH THE COOK INLET REGION LATE THIS AFTERNOON OR EARLY THIS
EVENING...AND THEN PASS THROUGH THE COPPER RIVER BASIN AND PRINCE
WILLIAM SOUND REGIONS AROUND MIDNIGHT THURSDAY NIGHT.

.ANALYSIS AND UPPER LEVELS...

THE 12 UTC SOUNDING AT ANCHORAGE SHOWED A FAIRLY ISOTHERMAL SATURATED
LAYER FROM THE SURFACE UP TO 775 MB...WITH AN EXTREMELY DRY LAYER
BETWEEN 550 MB AND 700 MB.  THE BOTTOM LINE...ANCHORAGE HAS SEEN
SEVERAL HOURS OF FREEZING RAIN THIS EVENING ATTRIBUTABLE TO WARM RAIN
PROCESSES DUE TO THE PRIME SNOW GROWTH ZONE BEING FAR TOO DRY.

ALOFT...THE STRONG UPPER RIDGE CONTINUES TO MOVE ONLY SLOWLY TO THE
EAST...WITH ITS AXIS JUST WEST OF THE ALCAN BORDER...WITH A BROAD
TROUGH SITUATED OVER THE BERING SEA AND NORTH PACIFIC WITH SEVERAL
EMBEDDED SHORTWAVES.  A STRONG NEGATIVE TILT SHORTWAVE IS MOVING
NORTHWARD AROUND A PRIMARY VORTEX OVER SIBERIA.  BETWEEN THIS
SHORTWAVE AND THE RIDGE AXIS...A STRONG SOUTHERLY JET IS BRINGING
VERY WARM WEATHER FROM THE EASTERN ALEUTIANS THROUGH SOUTHWEST
ALASKA.

AT THE SURFACE...THE PRIMARY WEATHER FEATURE CONTINUES TO BE THE 972
MB LOW CURRENTLY ABOUT 200 NM WEST OF HOOPER BAY IN THE NORTH BERING
SEA.  A WARM FRONT HAS MOVED WELL INLAND AND IS NOW SITUATED ALONG
THE ALASKA RANGE EXTENDING ALL THE WAY TO THE ALCAN BORDER.
SOUTHERLY FLOW HAS TAKEN OVER NEARLY ALL OF SOUTHCENTRAL AS THE
REGION IS SITUATED IN THE WARM SECTOR OF THIS SYSTEM.  A WEAK SURFACE
TROUGH IS LOCATED TO THE EAST OF THE KENAI PENINSULA ACROSS THE
NORTHERN GULF.  THE OTHER FEATURE ASSOCIATED WITH THIS LOW IS A COLD
FRONT WHICH IS CURRENTLY MOVING ALONG THE AKPEN EXTENDING INTO THE
FAR WESTERN GULF...AND WILL MAKE ITS WAY THROUGH THE REGION
TODAY...CROSSING SOUTHCENTRAL ALASKA LATE THIS AFTERNOON THROUGH THIS
EVENING.

.SHORT TERM FORECAST...

WEST OF THE ALASKA RANGE...STRONG COLD ADVECTION HAS TAKEN OVER TO
THE SOUTH OF THE SURFACE LOW...WITH WINDS TO STORM FORCE IN THE
NORTHERN AND EASTERN BERING...AND TO GALE FORCE ELSEWHERE. AS THESE
WINDS CONTINUE TO MOVE INLAND...BLOWING SNOW AND SNOW SHOWERS WILL
BECOME POSSIBLE THROUGH THIS EVENING AS TEMPERATURES BEGIN TO
COOL...WITH WINDS GUSTING UP TO 55 MPH AT TIMES.  FOR THE UPPER
KUSKOKWIM VALLEY...WARM AIR IS NEAR ITS PEAK EXTENT...AND THE COLUMN
SHOULD BEGIN COOLING SOON...EFFECTIVELY ENDING THE FREEZING RAIN
THREAT.  DUE TO THE STRONG DYNAMICS AND A TIGHT PRESSURE
GRADIENT...STRONG WINDS GUSTING TO 45 MPH WILL BE POSSIBLE IN THIS
REGION AS WELL.  ALONG THE BRISTOL BAY REGION THIS MORNING...WARMER
TEMPERATURES HAVE RESULTED IN MOSTLY RAIN WITH ISOLATED POCKETS OF
LIGHT FREEZING RAIN OR DRIZZLE...BUT WITH THE PASSAGE OF THE COLD
FRONT THIS MORNING...A SWITCHOVER TO SNOW SHOWERS WILL OCCUR ALONG
WITH WINDY CONDITIONS.

SOUTH AND EAST OF THE ALASKA RANGE...THE WARM FRONT AND UPSLOPE FLOW
ARE BOTH CONTRIBUTING TO HEAVY SNOWFALL WELL NORTH OF TALKEETNA ON
THE SOUTHERN SLOPES OF THE ALASKA RANGE...WHERE SNOW AMOUNTS ARE
STILL EXPECTED TO BE QUITE PRODIGIOUS.  ELSEWHERE...FOR THE MAT-SU
VALLEY...ANCHORAGE BOWL...AND THE KENAI PENINSULA...A DRY LAYER ALOFT
HAS RESULTED IN ONLY VERY LIGHT PRECIPITATION FALLING ACROSS THE
REGION.  AS THE COLD FRONT PASSES THROUGH LATE THIS
AFTERNOON...EXPECT WINDS TO SHIFT TO SOUTHWESTERLY AS COLD ADVECTION
TAKES OVER.  PRECIPITATION AMOUNTS SHOULD BE REMAIN LIGHT FOR
ANCHORAGE...WITH ONLY A BRIEF PERIOD OF SNOW ON THE BACKSIDE OF THE
FRONT.  FARTHER NORTH AND EAST...THE SOUTHWESTERN SLOPES OF THE
MATANUSKA VALLEY AND COPPER RIVER BASIN ZONES COULD SEE HEAVIER
AMOUNTS OF SNOW AS A LOW DEVELOPS INLAND AND MOVES TOWARDS THE ALCAN
BORDER TONIGHT.

.LONG TERM FORECAST...

SURFACE HIGH PRESSURE BUILDS ACROSS THE INTERIOR AHEAD OF ANOTHER
STRONG SYSTEM IN THE BERING SEA.  THE POSSIBILITY EXISTS OF STRONG
WINDS CREATING BLIZZARD CONDITIONS IN THE WESTERN ALEUTIANS ON THE
BACK SIDE OF THIS SYSTEM FOR SATURDAY...WITH STRONG SOUTHERLY FLOW
DEVELOPING IN THE EASTERN ALEUTIANS AND SOUTHWEST ALASKA AS A
TIGHTENING PRESSURE GRADIENT WILL EXIST BETWEEN THE HIGH OVER THE
MAINLAND AND THE LOW IN THE ALEUTIANS AND BERING SEA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...WINTER STORM WARNING...145
MARINE...GALE WARNING...121 129 132 140 141 150 155 160 165 170 171
                        176 180
         STORM WARNING...120 130 172 175 179 185
         HEAVY FREEZING SPRAY WARNING...140 185
FIRE WEATHER...NONE

CC MAR 09